Cork-board.



L. L. BENTLEY.

CORK BOARD.

APPLICATION FILED MAY 19, 1915.

WITNESSES INVENTOH cw a r .nnion.

LOUIS L. BENTLEY, 0F BEAVER FALLS, PENNSYLVANIA, ASSIGNOR TO ARMSTRONGCORK COMPANY, OF PITTSBURGH, SY'LVANIA,

PENNSYLVANIA, A CORPORATION 01'? PENN- CORK-BOARID.

menses.

Specification of Letters Patent.

Patented May 23, 1916.

Application filed May 19, 1915. Serial No. 29,036.

diagrammatic, showing means for determining the heat conductivity of thematerial; and Fig. 2 is a sectional view, also partly diagrammatic, ofthe same.

My invention provides a cork board which combines a relatively highdegree of structural strength with a relatively low weight per cubicfoot.

It also provides a cork board having a relatively high resistance toheat conductivity, which is more elastic than, and which is generallysuperior to, the cork board heretofore known.

Cork board is used to a large extent for heat insulation purposes, andparticularly in cold storage structures; and by the term cork board asused herein and in the claims I intend to cover not only boards ofthis'material, but also slabs, blocks, bricks, and other structuralshapes.

The best cork boards heretofore on the market have had a weight percubic foot of at least eight pounds, but notwithstanding this relativelyhigh density, the material is not homogeneous throughout, but containsto a very considerable extent, large air spaces or voids due toimperfect contact between the separate pieces or granules of cork. Thetensile strength of such product is usually not in excess of four poundsper square inch.

My improved cork board can be made with a weight of less than eightpounds per cubic foot; is much more compact and homogeneous than the oldproduct; has a tensile strength of not less than five pounds per squareinch of cross section, and has a very low heat conductivity. I havemanufactured this new product with a weight per cubic foot of but littlein excessof five pounds,

' and having a tensile strength of eight pounds per square inch of crosssection. Heat conductivity tests of this material show a heattransmission of less than five B. T. Uis'per square foot of one inchthickness in twentyfour hours for each one degree Fahrenheit differencein temperature, under cold storage conditions.

Cork board embodying my invention will 1n all cases have a weight percubic foot of from about four and eight-tenths pounds to seven andeight-tenths pounds; will have a tensile strength of not less than fivepounds per square inch of cross section, and usually very greatly inexcess of this figure and will have a heat transmission of less thanthat just' specified when tested by the well known hot-plate method.There are several varieties of the'hot plate method in use. The methodwhich I consider most accurate and which should be employed in testingmy improved material is shown in the accompanymg drawlng. In accordancetherewith, two

pieces or slabs 2 of the material are placed upon opposite sides of anelectrically heated hot plate 3, having a plurality of heating coils 4:arranged in multiple. To guard against heat losses, particularly at theedges of the test material, they are packed in a heat-insulatingmaterial 5, preferably loose kieselguhr.

6 designates cooling jackets having circulating baiiles 7, and placedone above the upper test piece and the other below the lower test piece.The two jackets have separate inlets 8 for water or brine and separateoutlets 9.

The numeral 10 designates an ameter, and

11 a voltmeter in the supply circuit for the heating coils.

12 is a constant voltage voltmeter which is connected to the centralportion 43* only of the middle heating coil, thus largely eliminatingerrors due to heat leakage at the edges.

13 is a millivoltmeter connected to a thermo-couple 142, placed in thatportion of the hot plate containing the section to which the voltmeter12 is connected:

In making a test, the following data is taken:

ET is the average temperature of the brine at the two inlets 8.

OT is the average temperature of the brine leaving the two outlets 9.

LV is the drop in voltage through the three coils 4.

CV is the drop in voltage through the portion 4: of the middle heatingcoil.

CT is the temperature at center of portion 4 as given by themillivoltmeter 13.

1 volt l ampere=1 watt.

1 watt in twenty-four hours=81.984 B. '1. U .s.

VoltageXamperage 8L984c=heat in B. T. U.s put in in twenty-four hours.

Then:

VoltageXamperageX81.984 thickness of test piece Degrees difference intemperaturexarea in sq. rt. of test piece Heat transmitted in B. T. U.sIper twenty-four hours per square foot area. per inch t ickness per eachdegree Fahrenheit difference in temperature.

I have stated that my improved material showed a heat transmission bythis test of less than five B. T. .U.s, per square foot of one inchthickness in twenty-four hours for.

each one degree F. difference in temperature, Whenthe colder surface is20 degrees F. and the hotter surface is 100 degrees F.

In the manufacture of my improved product the granulated cork is firstpreheated to a temperature higher than that which has heretofore beenused in the manufacture of this material. The effect of this hightemperature is to cause a large expansion of the cork particles, whichmay amount to one hundred per cent. or more. These expanded particlesare then placed in the mold, and into which the mass is pressed. Themolds are then subjected to a baking action at a higher temperature thanthat used in the preheating operation, cork being held under pressurewithin the molds in the meantime. The-effect of baking at a highertemperature, while the cork is under pressure, than that used in thepreheating, is to cause a further expansion of the individual particles,thus creating an internal pressure inthe mass within the mold, resultingin a closing up of the voids between the granules, a better contactbetween the granules, and a better cementing together of the entiremass. Any suitable process of manufacture which will give these resultsmay be employed. I prefer, however, to use the method which is describedand claimed in my application Serial No. 873,962, filed N ovember 25,1914. In accordance with that method the cork particles are firstpreheated to a temperature of not less than four hundred degreesFahrenheit, and which may run as high as five hundred fifty degreesFahrenheit. For this purpose the cork'may be fed through a heatingchamber such as a shell, to which the heat is applied externally. TheefiFect of preheating to this high temperature is to convert themoisture, and

1 other volatile matter within the cork into steam or vapor. The corkbeing brought up to this comparatively high temperature with relativerapidity the conversion of the volatile matter into steam or vaporcauses a large increase in volume, due to the expansion of the corkcells. This increase may amount to more than one hundred per cent. Thecork particles so treated, preferably while still at as high atemperature as practicable, are fed into a mold and are subjected topressure therein. The molds with the material confined therein are thensubjected to a baking action which preferably takes place at atemperature in excess of six hundred degrees Fahrenheit. The pressure isretained. until the material hasthoroughly set in the molds after thebaking operation is completed.

Material embodying my invention is readily distinguishable from theordinary cork board not only by the tests hereinbefore mentioned, butalso by its appearance. Not only at the surface, but throughout the massthe cork particles are much closer and in more uniform contact, causingthe cork board to present a more regular and homogeneous appearance.

y invention provides a cork board in which structural strength isobtained at a considerably lower weight per unit mass of material thanhas heretofore been possible. By the term structural strength as usedherein and in the claims, I mean sufiicient strength to enable thematerial to be selfsupporting and to be capable of practical use. Forinstance, with the cork boards heretofore known, when the weight percubic foot was less than about eight and one-half pounds, the resultingproduct possessed substantially no structural strength and was incapableof practical use. The invention also,

tofore on the market is quite marked in this respect. The corkboardsheretofore on the market show a very irregular surface, the particlesbeing separated from each other to a very considerable extent byintermediate void spaces. In the new product, while there isoccasionally a void space between the part of one expanded particle andthe part of an adjacent expanded particle, these voids are comparativelyfew in number both at the surface and throughout themass. It is thiscomparative freedom from voids and the fact that the peripheral surfacesof most of the expanded particles are in close contact with and cementedto the peripheral surfaces of adjacent particles which I have referenceto in characterizing the new product as one substantially free fromvoids.

I claim:

1. Cork board having a weight per cubic foot of less than seven andeight-tenths pounds, and possessing suflicient structural strength forpractical use in cold storage structures, substantially as described.

2. Cork board having a Weight per cubic foot of less than seven andeight-tenths pounds, and having a tensile strength of not less than fivepounds per square inch of cross section, substantially as described.

3. Cork board having, under the described conditions, a heattransmission of less than five B. U.s per square foot of one inchthickness in twenty-four hours for each degree Fahrenheit difference intemperature, by the described h0t+plate test, substantially asdescribed.

4. Corkboard having, under the conditions described, a heat transmissionof less than five B. T. /U.s per square foot of one inch thickness intwenty-four hours for each degree F. d iflerence in temperature by thedescribed hot plate test, and having a Weight per cubic foot of lessthan seven and eighttenths pounds.

5. Corkboard having, under the conditions described, a heat transmissionof less than five B. T. U.s per square foot of one inch thickness intwenty-four hours for each degree F. difference in temperature by thedescribed hot plate test, and having a tensile strength of not less thanfive pounds per square inch of cross section.

6. Corkboard having, under the conditions section and described, a heattransmission of less than five B. T. U.s per square foot of one inchthickness in twenty-four hours for each degreeF. difference intemperature by the described hot plate test, and having a Weight percubic foot of less than seven and eighttenths pounds, and a tensilestrength of not less than five pounds per square inch of cross section.

7. A corkboard having a Weight per cubic foot of less than seven andeight-tenths pounds and substantially free from voids. 8. Corkboardhaving a tensile strength of not less than five pounds per square inchof cross section and substantially free from voids.

9. Corkboard having a Weight per cubic foot of less than seven andeight-tenths pounds and a tensile strength of not less than five poundsper square inch of cross which is substantially free from voids.

In testimony whereof, I have hereunto set my hand.

Witnesses FRED BOYLE, F. D. MILLER.

